1. Field of the Invention
The present invention relates to a fuel burner for coal in the fine powder form (hereinafter referred to as the pulverized coal) used for boilers.
2. Description of the Prior Art
Fossile fuels contain the nitrogen (N) component besides the fuel components such as carbon and hydrogen. In the case of coal in particular, the N content is great in comparison with gas fuels and liquid fuels. Hence, the quantity of the nitrogen oxides (hereinafter referred to as NO.sub.x) generated upon combustion of coal is greater than when a liquid fuel is burnt, and it has been desired to reduce this NO.sub.x as much as possible.
Conventional combustion methods to restrict the formation of NO.sub.x include a two-stage combustion method which arranges the primary fuel nozzle jetting the first fuel with a smaller air ratio at an inner cylindrical portion and the second fuel nozzle jetting the second fuel with a large air ratio at an outer cylindrical portion which is located at the outer circumferential portion of the inner cylindrical portion.
Japanese Laid Open Utility-model Application No. 54-105031 (1979), published on July 24, 1979, "Previously mixed combustion burner" is concerned with such a two-stage combustion method.
There is enthusiastic desire to supply a fuel and air jet method and apparatus for a pulverized coal, lower NO.sub.x burner which is particularly suitable for reducing much of the NO.sub.x generated at the combustion of the pulverized coal.